This application relates to refrigerant systems having enhancement features and extended functionality. Further, this application relates to refrigerant systems incorporating multiple compressors, such as tandem compressors, that may include an economizer cycle, a bypass circuit and a variable speed drive, as well as to refrigerant systems incorporating a reheat function, and wherein a control algorithm is utilized to provide diagnostic and prognostic information with regard to each of these enhancement features.
Heating, ventilation, air conditioning and refrigeration (HVAC&R) systems are utilized to condition various environments. The HVAC&R systems typically use a refrigerant circulating throughout a closed-loop circuit and are applied as air conditioners, heat pumps, refrigeration units, etc. Various enhancement techniques and system configurations are known and implemented to provide a required performance over a wide spectrum of environmental conditions to satisfy diverse thermal load demands.
In a very basic refrigerant system, a compressor compresses a refrigerant and delivers it downstream to a condenser. Refrigerant passes from the condenser to an expansion device, and from the expansion device to an evaporator. From the evaporator, refrigerant returns to the compressor. This basic system is typically supplemented and enhanced by a number of different options and features to satisfy application requirements.
One such enhancement is the use of tandem compressors. Tandem compressors include a plurality of compressors each receiving refrigerant from a common suction manifold, each separately compressing the refrigerant and delivering the refrigerant to a common discharge manifold. Each of these compressors may be independently turned on or off to vary refrigerant system capacity. In this manner, the capacity provided by the compressor subsystem to the overall refrigerant system can be tailored to the thermal load demands in the conditioned space. Quite often, tandem compressor configurations include oil and vapor equalization lines for functionality and reliability enhancement.
Another option to vary refrigerant system capacity, which can be used within a tandem compressor arrangement, includes the use of a compressor unloading function. One commonly employed compressor unloading function may selectively deliver at least a portion of compressed (partially or fully) refrigerant back to a suction line. In this manner, the amount of compressed refrigerant delivered through the refrigerant system is reduced when a part-load capacity is demanded. Other compressor unloading schemes are also known in the art. As known, compressor unloading may be used outside tandem compressor applications as well.
Another performance enhancement feature, which can be employed with tandem compressors, is the use of a variable speed drive to vary the speed of the compressor motor. By providing a variable frequency control for varying the compressor motor speed, the amount of the compressed refrigerant delivered throughout the system can be varied accordingly. Again, this allows the refrigerant system designer to tailor the provided capacity to a desired capacity demand. As above, a variable speed compressor may be used outside tandem compressor arrangements.
One other option of performance boost for a refrigerant system, which can be incorporated within tandem compressor subsystems, is the use of an economizer cycle. The economizer cycle selectively taps a portion of the refrigerant downstream of the condenser and upstream of the expansion device, and passes that tapped refrigerant to a separate economizer expansion device. This tapped partially expanded refrigerant is then utilized to cool a refrigerant circulating through the main circuit in an economizer heat exchanger. By providing this extra subcooling, the capacity and/or efficiency of the refrigerant system are increased. As known, an economizer cycle can employ a single compressor or multiple compression stages operating in sequence. Once again, this performance enhancement feature can be used outside tandem compressors as well.
Another optional refrigerant system feature, which may or may not be used in conjunction with the tandem compressors, is a reheat function. In a reheat cycle, refrigerant, which is warmer than the refrigerant flowing through the evaporator, is directed through a reheat heat exchanger positioned on the refrigerant path upstream of the evaporator. The air to be conditioned may be cooled (and dehumidified) in the evaporator to a temperature below than desired. That air then passes over the reheat heat exchanger where it is warmed back to the target temperature. However, having been overcooled in the evaporator, the air would have much lower moisture content than if it had only been cooled to the target temperature. Various reheat system configurations are known in the HVAC&R industry, and this invention is not intended to reference to any particular schematic, but rather refers to a generic mechanical dehumidification reheat concept utilizing primary refrigerant circulating throughout a refrigerant system. Once again, the reheat function can be used outside tandem compressor applications.
Various diagnostic features are known in the prior art. However, the prior art has not provided a system for diagnostic and prognostic features based on staged operation of compressors and other associated system components, when anyone of the several tandem compressors or other associated system components, may be experiencing a problem. Further, controls for optimizing refrigerant system operation when one of the tandem compressors may be running in an undesirable manner (e.g., outside the specified envelope), have also not been provided.